Precision casting mold and method of producing the same

ABSTRACT

Provided is a precision casting mold including a core and an outer mold, and the outer mold is made up of: a prime layer which is formed from a slurry film obtained by drying slurry for the precision casting mold including a silica sol having a particle size of 20 nm; and a multi-layered backup layer which is formed on the outside of the prime layer by repeatedly forming a first backup layer obtained by forming and drying a slurry layer formed from the slurry for the precision casting mold and a stucco layer in which stucco particles as a stucco material having particle size distribution, in which a mixing ratio of the fine particles having a particle size of 50 to 500 μm is 1; the mixing ratio of the medium particles having a particle size of 0.5 to 2 mm is 1 to 16; and the mixing ratio of the coarse particles having a particle size of 2 to 4 mm is 1 to 40, is adhered to the slurry layer.

FIELD

The present invention relates to a precision casting mold and a methodof producing the same.

BACKGROUND

There is a precision casting method used in the case of producing a castproduct with high precision as a casting method of producing a castproduct. In the precision casting method, as disclosed in PatentLiterature 1, slurry is applied around a lost foam pattern (wax pattern)having the same shape as a molded component and then a first stucco(flour) layer is adhered to it and is then subjected to a dryingtreatment. Thereafter, three operations of the application of theslurry, the adhesion of the stucco, the drying are repeatedly performed,thereby producing a pattern for covering the outside (outer mold) of thecast product.

Here, the precision casting mold is formed in such a manner that the waxpattern is placed in slurry mainly including a silica sol, the slurry isadhered to the surface of the wax pattern, and then the slurry is dried.

Since the slurry adhered by single operation is only less and thin, theoperation is repeatedly performed from several to ten times to obtainthe thickness. In addition, coarse particles called a stucco materialare sprinkled and adhered to the surface of the slurry to fast performthe drying, quickly ensure the thickness, or prevent dry cracks.Therefore, a dense layer and a coarse particle layer are repeated in thecross-sectional structure of the mold.

For example, the silica sol is a solution in which spherical silicaparticles having a particle size of about 20 nm are dispersed. When theultrafine silica particles are adhered to the surface of relatively fineparticles (from several microns to scores of microns) and coarseparticles (stucco) (hundreds of microns to several millimeters) such aszircon or alumina contained in the slurry during the drying and aretightly bonded to each other by drying and heat treatment, the shape ofthe mold is maintained and strength is also held, so that it is possibleto use as a mold.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No.2001-18033

SUMMARY Technical Problem

However, in general, it is sufficient to produce a mold using theabove-described silica sol (solution in which ultrafine silica particlesare dispersed), but it is necessary to hold a molten metal to control acrystal precipitation direction in, for example, a production of aunidirectional solidified blade. As a result, holding time at a hightemperature (for example, about 1550° C.) becomes longer. In this case,there is a problem that the silica serving as a binder is softened dueto the high-temperature holding, resulting in occurring deformation ofthe mold.

In such a production of the unidirectional solidified blade referredherein, the blade is generally produced in such a manner that the moldis placed in a vacuum heater and is heated and held at a temperatureequal to or higher than a melting point of the molten metal, and thusthe molten metal is poured into the mold and the mold is taken out fromthe heater while being controlled for the pulling toward a lower side,so that the molten metal is cooled and solidified from the lower side.

Accordingly, for example, in the production of the unidirectionalsolidified blade, a mold is required which is not deformed even in thecase of being held at the high temperature (for example, about 1550° C.)over a long period.

The present invention has been achieved in consideration of the aboveproblem and an object thereof is to provide a precision casting moldwhich is not deformed even in the case of being held at the hightemperature for a long period and a method of producing the same.

Solution to Problem

According to a first aspect of the present invention in order to solvethe above-mentioned problems, there is provided a precision casting moldwhich is used to produce a cast product, including: a core having ashape corresponding to an internal hollow portion of the cast product;and an outer mold corresponding to a shape of an outer peripheralsurface of the cast product, wherein the outer mold is made up of: aprime layer which is formed on an inner peripheral surface and is formedfrom a slurry film obtained by drying slurry for the precision castingmold; and a multi-layered backup layer which is formed on the outside ofthe prime layer by repeatedly forming a backup layer obtained by formingand drying a slurry layer formed from the slurry for the precisioncasting mold and a stucco layer in which stucco particles as a stuccomaterial having particle size distribution, in which a mixing ratio offine particles having a particle size of 50 to 500 μm is 1; the mixingratio of medium particles having a particle size of 0.5 to 2 mm is 1 to16; and the mixing ratio of coarse particles having a particle size of 2to 4 mm is 1 to 40, are adhered to the slurry layer.

According to a second aspect of the present invention, there is providedthe precision casting mold according to the first aspect, wherein theprime layer has a stucco layer in which stucco particles as a stuccomaterial having particle size distribution, in which a mixing ratio offine particles having a particle size of 50 to 500 μm is 1; a mixingratio of medium particles having a particle size of 0.5 to 2 mm is 1 to16; and a mixing ratio of coarse particles having a particle size of 2to 4 mm is 1 to 40, are adhered to the slurry layer formed from theslurry for the precision casting mold.

According to a third aspect of the present invention, there is provideda method of producing a precision casting mold which is used to producea cast product, the method including: a first film forming process inwhich a precision casting wax pattern is immersed and pulled upinto/from slurry for the precision casting mold and then a dryingtreatment is performed, thereby forming a prime layer, which is formedfrom a slurry film, on a surface of the wax pattern; a second filmforming process in which stucco particles as a stucco material havingthe particle size distribution, in which the mixing ratio of the fineparticles having the particle size of 50 to 500 μm is 1; the mixingratio of the medium particles having the particle size of 0.5 to 2 mm is1 to 16; and the mixing ratio of the coarse particles having theparticle size of 2 to 4 mm is 1 to 40, is sprinkled on a surface of theslurry after the wax pattern formed with the prime layer is immersed andpulled up into/from the slurry for the precision casting mold and then adrying treatment is performed, thereby forming a backup layer; a moldedbody forming process in which the second film forming process of formingthe backup layer is repeated more than once, thereby obtaining a moldedbody formed with a multi-layered backup layer; a wax removing process inwhich wax of the wax pattern is melted and removed from the obtainedmolded body; and a mold firing process in which the molded body obtainedafter the wax removal is subjected to a firing treatment, therebyobtaining a mold.

According to a fourth aspect of the present invention, there is providedthe method of producing the precision casting mold according to thethird aspect, wherein the stucco particles as a stucco material havingparticle size distribution, in which a mixing ratio of fine particleshaving a particle size of 50 to 500 μm is 1; a mixing ratio of mediumparticles having a particle size of 0.5 to 2 mm is 1 to 16; and a mixingratio of coarse particles having a particle size of 2 to 4 mm is 1 to40, is adhered to the slurry layer formed from the slurry for theprecision casting mold to form a stucco layer and the stucco layer isdried during the first film forming process.

Advantageous Effects of Invention

According to the present invention, a stucco material has particle sizedistribution in which the mixing ratio of fine particles having aparticle size of 50 to 500 μm is 1; the mixing ratio of medium particleshaving a particle size of 0.5 to 2 mm is 1 to 16; and the mixing ratioof coarse particles having a particle size of 2 to 4 mm is 1 to 40, andthus it is possible to obtain an effect that strength of a mold isimproved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a dried molded body which is anouter mold.

FIG. 2 is a configuration diagram of another dried molded body which isan outer mold.

FIG. 3 is a flowchart illustrating an example of processes in a castingmethod.

FIG. 4 is a flowchart illustrating an example of processes in a methodof producing a mold.

FIG. 5 is an explanatory diagram schematically illustrating a process ofproducing a core.

FIG. 6 is a perspective view schematically illustrating a part of ametal mold.

FIG. 7 is an explanatory diagram schematically illustrating a process ofproducing a wax pattern.

FIG. 8 is an explanatory diagram schematically illustrating aconfiguration in which slurry is applied on the wax pattern.

FIG. 9 is an explanatory diagram schematically illustrating a process ofproducing the outer mold.

FIG. 10 is an explanatory diagram schematically illustrating someprocesses in the method of producing the mold.

FIG. 11 is an explanatory diagram schematically illustrating someprocesses in a casting method.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail withreference to the drawings. Furthermore, the present invention is notlimited to the following description. Further, components in thefollowing description include those which are easily conceived bypersons skilled in the art, those which are substantially identicalthereto, and those in a scope of so-called equivalents.

FIG. 1 is a configuration diagram of a dried molded body which is anouter mold. FIG. 2 is a configuration diagram of another dried moldedbody which is an outer mold.

As illustrated in FIG. 1, a precision casting mold is a precisioncasting mold to be used to produce a cast product and includes a corehaving a shape corresponding to an internal hollow portion of the castproduct and an outer mold corresponding to a shape of an outerperipheral surface of the cast product, and the outer mold is made upof: a prime layer (first dried film: first slurry layer) 101A which isformed on an inner peripheral surface and is formed from a slurry filmobtained by drying slurry for the precision casting mold including asilica sol having a particle size of 20 nm; and a multi-layered backuplayer 105A which is formed on the outside of the prime layer (firstdried film) 101A by repeatedly forming a first backup layer (seconddried film) 104-1 obtained by forming and drying a slurry layer 102formed from the slurry for the precision casting mold and a stucco layer103 in which stucco particles as a stucco material having particle sizedistribution, in which a mixing ratio of fine particles having aparticle size of 50 to 500 μm is 1; the mixing ratio of medium particleshaving a particle size of 0.5 to 2 mm is 2 to 16; and the mixing ratioof coarse particles having a particle size of 2 to 4 mm is 5 to 40, areadhered to the slurry layer 102.

Here, the silica sol is used as the slurry for the precision castingmold for forming the slurry in the present invention, but the presentinvention is not limited thereto and can use, for example, fine aluminaparticles (ultrafine alumina particles) or zirconia fine particle ofhigh purity ultrafine particles, which are subjected to mono-dispersionusing, for example, a ball mill as a dispersion means.

The term “mono-dispersion” used herein refers to a state of beingmono-dispersed into 0.5 μm even in a result of a dispersion treatmentwhen the slurry is formed using, for example, fine alumina particleshaving a particle size of about 0.5 μm.

Here, the particle size of the fine alumina particles or the zirconiafine particles is 1.0 μm or smaller and more preferably may be in therange of 0.3 to 0.6 μm.

In the present invention, the reason why the fine alumina particles orthe zirconia fine particles are preferably 1.0 μm or smaller in size isbecause results of a bending strength test are undesirable when the finealumina particles or the zirconia fine particles exceed 1.0 μm in size.

In addition, for example, the slurry for the precision casting mold maybe obtained by dispersing the silica sol into the slurry in which thefine alumina particles (ultrafine alumina particles) of the high purityultrafine particles are mono-dispersed using, for example, the ball millas the dispersion means.

Zircon powders (for example, having a size of 350-mesh) as flour areadded, thereby obtaining the slurry for the precision casting mold.

Further, in the present invention, a case where the flour is not addedmay be also acceptable.

Here, polycarboxylic acid salts (for example, ammonium salts) are usedto be mono-dispersed as a dispersing agent.

In addition, a ball mill using, for example, balls having a diameter of10 to 20 mm can be exemplified as the dispersion means, but thedispersion means is not limited thereto as long as being a means thatmono-disperses.

In the present invention, it is important to obtain good slurry bymono-dispersing the fine alumina particles or zirconia fine particlesserving as the binder.

Furthermore, in the present invention, alumina stucco particles are usedas a stucco material in which the mixing ratio of fine particles of 50to 500 μm is 1; the mixing ratio of medium particles of 0.5 to 2 mm is 1or more and is more preferably 2 to 16; and the mixing ratio of coarseparticles of 2 to 4 mm is 1 or more and is more preferably 2 to 40.

In the present invention, the stucco material is obtained by mixingdifferent particle sizes, so that particles of the stucco portion aredensely filled. As a result, strength of the mold can be improved.

Hereinafter, the mixing of the stucco particles was examined.

As indicated in Table 1, the strength of the mold was 10 MPa inComparative Example 1 in which the conventional stucco particles of 1 to3 mm (central particle size of 2 mm) were distributed.

In contrast, the strength was examined when the fine particles of 50 to500 μm, the medium particles of 0.5 to 2 mm, and the coarse particles of2 to 4 mm were changed in mixing ratio, respectively.

Results of the test are indicated in Table 1.

TABLE 1 Stucco particles Fine Medium Coarse particles particlesparticles Strength (50 to 500 μm) (0.5 to 2 mm) (2 to 4 mm) (MPa)Comparative Particles of 1 to 3 mm distributed 10 Example 1 (centralparticle size of 2 mm) Test 1 1 1 1 13 Test 2 1 3 2 15 Test 3 1 2 3 14

In Table 1, the strength was 13 MPa in Test 1 in the case of usingstucco particles in which the mixing ratio of fine particles of 50 to500 μm was 1, the mixing ratio of the medium particles of 0.5 (500 μm)to 2 mm was 1, and the mixing ratio of the coarse particles of 2 to 4 mmwas 1.

In addition, the strength was 15 MPa in Test 2 in the case of usingstucco particles in which the mixing ratio of fine particles of 50 to500 μm was 1, the mixing ratio of the medium particles of 0.5 (500 μm)to 2 mm was 2, and the mixing ratio of the coarse particles of 2 to 4 mmwas 3.

In addition, the strength was 14 MPa in Test 3 in the case of usingstucco particles in which the mixing ratio of fine particles of 50 to500 μm was 1, the mixing ratio of the medium particles of 0.5 (500 μm)to 2 mm was 2, and the mixing ratio of the coarse particles of 2 to 4 mmwas 3.

From these results, the strength was excellent in the mixing ratio as inTests 1 and 2.

In addition, it was found that the strength of the mold, which wasgenerally produced as a trial, is about 10 MPa and the particles of thestucco portion were densely filled by mixing the different particlesizes, resulting in improving the strength of the mold.

Here, as examples of the stucco material, spinel stucco particles,mullite stucco particles, zircon stucco particles or the like can beused in addition to the alumina stucco particles.

In the present invention, since the stucco material is obtained bysetting the mixing ratio of the particle sizes to a predetermined mixingratio, it is possible to significantly improve the strength of the moldcompared to that of the conventional mold.

Due to the improvement in strength of the mold, it is possible to makethe mold thinner, to reduce the number of layers, to shorten a moldproduction period, and to reduce production cost.

In addition, since a temperature gradient can be increased duringsolidification, it can be expected to improve a cast product yield andto improve strength properties.

Next, a method of producing the precision casting mold will be describedwith reference to FIGS. 1 and 2.

(First Film Forming Process)

First, in the first film forming process, a wax pattern 30 is immersedand then pulled up into/from the slurry for the precision casting mold(hereinafter, referred to as “slurry”) including the silica sol, andexcess slurry is dropped. Thereafter, a slurry film (first dried film)is obtained on the surface of the wax pattern 30 by a drying treatment.

In FIG. 1, the slurry film is the prime layer 101A which comes incontact with the surface of the wax pattern 30.

(Second Film Forming Process)

Next, the wax pattern 30 having the prime layer 101A is immersed and isthen pulled up into/from the slurry, and the excess slurry is dropped,thereby forming the slurry layer (second layer) 102. Stucco particles asa stucco material having the particle size distribution, in which themixing ratio of the fine particles having a particle size of 50 to 500μm is 1; the mixing ratio of the medium particles having a particle sizeof 0.5 to 2 mm is 2 to 16; and the mixing ratio of the coarse particleshaving a particle size of 2 to 4 mm is 5 to 40, are sprinkled (stuccoed)on the wet slurry layer (second layer) 102, thereby forming the stuccolayer (first layer) 103 adhered with the stucco material. A laminatedstructure of the slurry layer 102 and the stucco layer (first layer) 103is dried, so that the first backup layer (second dried film) 104-1 isformed on the prime layer (first dried film) 101.

(Molded Body Forming Process)

The similar operation as the second film forming process of forming thefirst backup layer 104-1 is repeated more than once (for example, 6 to10 times), thereby obtaining a dried molded body 106A which is the outermold having a predetermined thickness of the multi-layered backup layer105A in which the slurry layer ((n+1)-th layer) 102 and the stucco layer(n-th layer) 103 are alternately laminated.

The dried molded body is put in, for example, an autoclave of 150° C.,so that wax constituting the wax pattern 30 is melted and then isdischarged.

Thereafter, the pattern is subjected to a heat treatment at 1,000° C.,thereby obtaining the precision casting mold.

In the obtained precision casting mold, since the stucco particleshaving the particle size distribution, in which the mixing ratio of thefine particles having a particle size of 50 to 500 μm is 1; the mixingratio of the medium particles having a particle size of 0.5 to 2 mm is 2to 16; and the mixing ratio of the coarse particles having a particlesize of 2 to 4 mm is 5 to 40, are used as the stucco material, it ispossible to improve the strength of the obtained mold.

In addition, as illustrated in FIG. 2, a prime stucco layer 101 badhered with the stucco particles as the stucco material having theparticle size distribution, in which the mixing ratio of the fineparticles having a particle size of 50 to 500 μm is 1; the mixing ratioof the medium particles having a particle size of 0.5 to 2 mm is 2 to16; and the mixing ratio of the coarse particles having a particle sizeof 2 to 4 mm is 5 to 40, may be formed on a prime slurry layer 101 a ina prime layer 101B and may be then dried, thereby forming the primelayer 101B.

Further, as in the prime layer 101B, when the stucco material isadhered, it is possible to obtain a dried molded body 106B of an outermold having a multi-layered backup layer 105B in which the slurry layerand the stucco layer 103 of the multi-layered backup layer 105B have thesame laminated number (n layers).

In the present invention, although zircon powders were used as flour, itis possible to obtain the similar precision casting mold even whenalumina powders other than the zircon powders are used as the flour andalumina stucco particles are used instead of the zircon stucco particlesas a stucco material.

Further, the relation between the flour and the stucco material is notlimited, but either of the zircon powders or the alumina powders may beused as the flour and either of the zircon stucco particles or thealumina stucco particles may be used as the stucco material.

Although the particle size of the flour is 350-mesh, the presentinvention is not limited thereto, but preferably uses particles of, forexample, about 5 to 80 μm and particles having an average particle sizeof, for example, 50 μm or smaller.

A casting method using the precision casting mold according to thepresent invention will be described below.

FIG. 3 is a flowchart illustrating an example of processes in thecasting method. The casting method will be described below withreference to FIG. 3. Here, the processes illustrated in FIG. 3, may befully automatically executed or may be executed in such a manner that anoperator operates each of apparatuses for executing each of theprocesses. In the casting method of the present embodiment, a mold isproduced (step S1). The mold may be previously produced or may beproduced every time a casting process is executed.

The method of producing the mold of the present embodiment to beexecuted in step S1 will be described below with reference to FIGS. 4 to10. FIG. 4 is a flowchart illustrating an example of processes in themethod of producing the mold. Here, processes illustrated in FIG. 4, maybe fully automatically executed or may be executed in such a manner thatan operator operates each of apparatuses for executing each of theprocesses.

In the method of producing the mold, a core is produced (step S12). Thecore has a shape corresponding to an internal hollow of a cast productto be produced with the mold. That is, the core is disposed at a portioncorresponding to the internal hollow of the cast product and preventsinflow of a metal, which is a material for the cast product, duringcasting. Hereinafter, a process of producing the core will be describedwith reference to FIG. 5. FIG. 5 is an explanatory diagram schematicallyillustrating the process of producing the core. In the method ofproducing the mold, as illustrated in FIG. 5, a metal mold 12 isprepared (step S101). The metal mold 12 has a hollow regioncorresponding to the core. The hollow portion of the core is a convexportion 12 a. Further, in FIG. 5, the metal mold 12 is illustrated incross section, but the metal mold 12 becomes basically the hollow forcovering an entire periphery of the region corresponding to the core,except for an opening through which a material is poured into a spaceand a hole through which air is discharged. In the method of casting themold, as indicated by an allow 14, ceramic slurry 16 is poured into theinside of the metal mold 12 from the opening through the material ispoured into the space of the metal mold 12. Specifically, a core 18 isproduced by so-called injection molding which sprays the ceramic slurry16 into the inside of the metal mold 12. In the method of producing themold, after the core 18 is produced inside the metal mold 12, the core18 is detached from the metal mold 12 and the detached core 18 is placedin a firing furnace 20, thereby being fired. Thus, the core 18 formed ofa ceramic is fired and hardened (step S102). In the method of castingthe mold, the core 18 is produced in the manner described above.Further, the core 18 is formed of a material capable of being removedwith a core removing treatment such as a chemical treatment after thecast product is hardened.

In the method of producing the mold, after the core 18 is produced, anexternal metal mold is produced (step S14). The external metal mold hasa shape in which an inner peripheral surface thereof corresponds to theouter peripheral surface of the cast product. The metal mold may beformed of a metal or may be formed of a ceramic. FIG. 6 is a perspectiveview schematically illustrating a part of the metal mold. A metal mold22 a illustrated in FIG. 6 is configured such that a concave portionformed on the inner peripheral surface corresponds to the outerperipheral surface of the cast product. Further, in FIG. 6, only themetal mold 22 a is illustrated, but corresponding to the metal mold 22a, a metal mold corresponding to the metal mold 22 a is also produced ina direction to close the concave portion formed on the inner peripheralsurface. The method of producing the mold is a type in which the innerperipheral surface corresponds to the outer peripheral surface of thecast product when two metal molds are fitted to each other.

In the method of producing the mold, after the external metal mold isproduced, a wax pattern is produced (step S16). The description will bemade below with reference to FIG. 7. FIG. 7 is an explanatory diagramschematically illustrating a process of producing the wax pattern. Inthe method of producing the mold, the core 18 is installed at apredetermined position of the metal mold 22 a (step S110). Thereafter, ametal mold 22 b corresponding to the metal mold 22 a covers a surface onwhich the concave portion of the metal mold 22 a is formed, so that themetal molds 22 a and 22 b surround the periphery of the core 18 and aspace 24 is formed between the core 18 and the metal molds 22 a and 22b. In the method of producing the mold, as indicated by an arrow 26, apouring of a WAX 28 starts to be poured from a pipe connected to thespace 24 into the inside of the space 24 (step S112). The WAX 28 is, forexample, wax of a relatively low-melting point material which is meltedwhen being heated to a predetermined temperature or higher. In themethod of producing the mold, the entire region of the space 24 isfilled with the WAX 28 (step S113). Thereafter, the WAX 28 enclosesaround the core 18 by solidifying the WAX 28, thereby forming the waxpattern 30. The wax pattern 30 is a wax pattern in which a portionformed of the WAX 28 has basically the same shape as the cast product ofthe production object. Thereafter, in the method of producing the castproduct, the wax pattern 30 is separated from the metal molds 22 a and22 b and then a sprue 32 is attached to the wax pattern (step S114). Thesprue 32 is a mouth into which a molten metal, which is a metal meltedduring casting, is introduced. In the method of producing the mold, thewax pattern 30 formed of the WAX 28 is produced in the manner describedabove so as to have the same shape as the cast product and include thecore 18 therein.

In the method of producing the mold, after the wax pattern 30 isproduced, slurry is applied (dipped) (step S18). FIG. 8 is anexplanatory diagram schematically illustrating a configuration in whichthe slurry is applied on the wax pattern. In the method of producing themold, as illustrated in FIG. 8, the wax pattern 30 is immersed into astorage portion 41, in which slurry 40 is stored, and then is driedafter being taken out therefrom (step S19). Thus, the prime layer 101Acan be formed on the surface of the wax pattern 30.

Here, the applied slurry in step S18 is slurry which is directly appliedon the wax pattern 30. A silica sol is used for the slurry 40. In theslurry 40, for example, zirconia having refractory fine particles ofabout 350-mesh is preferably used as flour. In addition, polycarboxylicacid salts are preferably used as a dispersing agent. In addition, atrace of an antifoaming agent (silicon-based substance) or a wettabilityimproving agent of, for example, 0.01% is preferably added to the slurry40. By the addition of the wettability improving agent, adhesiveproperty of the slurry 40 can be improved with respect to the waxpattern 30.

In the method of producing the mold, as illustrated in FIG. 8, a slurryapplication is performed with the slurry 40, and the applied slurry isdried, so that the wax pattern 30 having the prime layer (first driedfilm) 101A is further applied (dipped) with the slurry (step S20). Asillustrated in FIG. 9, stuccoing process of sprinkling the stuccoparticles as a stucco material 54 having the particle size distribution,in which the mixing ratio of the fine particles having a particle sizeof 50 to 500 μm is 1; the mixing ratio of the medium particles having aparticle size of 0.5 to 2 mm is 2 to 16; and the mixing ratio of thecoarse particles having a particle size of 2 to 4 mm is 5 to 40 isperformed on the surface of the wet slurry (step S21). Thereafter, thestucco material adhered to the surface of the slurry layer is dried,thereby forming the first backup layer (second dried film) 104-1 on theprime layer (first dried film) 101A (step S22).

A process of determining whether the similar operation as the formingprocess of the first backup layer (second dried film) 104-1 is repeatedmore than once (for example, n: six to ten times) is performed (stepS23). An n-th backup layer 104-n is laminated by a predetermined numberof times (n) (step S23: Yes), thereby obtaining the dried molded body106A which is the outer mold formed with the multi-layered backup layer105A having the thickness of, for example, 10 mm.

In the method of producing the mold, after the dried molded body 106Ahaving the multilayer structure is obtained which is formed with theprime layer 101A and the multi-layered backup layer 105A, the driedmolded body 106A is subjected to a heat treatment (step S24).Specifically, the WAX between the outer mold and the core is removed,and the outer mold and the core are further fired. The description willbe made below with reference to FIG. 10. FIG. 10 is an explanatorydiagram schematically illustrating some processes of the method ofproducing the mold. In the method of producing the mold, as illustratedin step S130, the dried molded body 106A which is the outer mold havingthe multilayer structure formed with the prime layer 101A and themulti-layered backup layer 105A is put in an autoclave 60 and then isheated. The inside of the autoclave 60 is filled with pressurized steam,and thus the wax pattern 30 inside the dried molded body 106A is heatedby the pressurized steam. Thus, the WAX constituting the wax pattern 30is melted and a melted WAX 62 is discharged from a space 64 surroundedby the dried molded body 106A.

In the method of producing the mold, when the melted WAX 62 isdischarged from the space 64, as illustrated in step S131, a mold 72 isproduced in which the space 64 is formed in a region filled with the WAXbetween the dried molded body 106A which is the outer mold and the core18. Thereafter, in the method of producing the mold, as illustrated instep S132, the mold 72 having the space 64 formed between dried moldedbody 106A which is the outer mold and the core 18 is heated by a firingfurnace 70. Thus, in the mold 72, a water component or an unnecessarycomponent contained in the dried molded body 106A which is the outermold is removed and an outer mold 61 is formed by being further firedand cured. In the method of producing the cast product, the mold 72 isproduced in the manner described above.

The casting method will be continuously described with reference toFIGS. 3 and 11. FIG. 11 is an explanatory diagram schematicallyillustrating some processes of the casting method. In the castingmethod, after the mold is produced in step S1, the mold is pre-heated(step S2). For example, the mold is disposed in a furnace (vacuumfurnace, firing furnace) and is heated to 800° C. or higher and 900° C.or lower. By the pre-heating, it is possible to suppress the damage ofthe mold when the molten metal (melted metal) is poured into the mold atthe time of producing the cast product.

In the casting method, after the mold is pre-heated, the molten metal ispoured (step S3). That is, as illustrated in step S140 of FIG. 11, amolten metal 80, that is, a dissolved raw material (for example, steel)of the cast product is poured between the outer mold 61 and the core 18from the opening of the mold 72.

In the casting method, after the molten metal 80 poured into the mold 72is solidified, the outer mold 61 is removed (step S4). That is, asillustrated in step S141 of FIG. 11, after the molten metal 80 ishardened inside the mold 72 and becomes a cast product 90, the outermold 61 is crushed and is then removed from the cast product 90 as afragment 61 a.

In the casting method, after the outer mold 61 is removed from the castproduct 90, a core removing treatment is performed (step S5). That is,as illustrated in step S142 of FIG. 11, the cast product 90 is put in anautoclave 92 and is subjected to the core removing treatment, so thatthe core 18 inside the cast product 90 is dissolved and a dissolved core94 is discharged from the inside of the cast product 90. Specifically,the cast product 90 charged into an alkaline solution inside theautoclave 92 is repeatedly pressurized and depressurized, so that thedissolved core 94 is discharged from the cast product 90.

In the casting method, after the core removing treatment is performed, afinishing treatment is performed (step S6). That is, the finishingtreatment is performed on the surface or the interior of the castproduct 90. Furthermore, in the casting method, inspection of the castproduct is performed along with the finishing treatment. Thus, asillustrated in step S143 of FIG. 11, a cast product 100 can be produced.

In the casting method of the present embodiment, as described above, themold is produced by a lost-wax casting method using WAX (wax), therebyproducing the cast product. Here, in the method of producing the mold,the casting method, and the mold of the present embodiment, the outermold having the multilayer structure in which the outside of the mold isformed in such a manner that the prime layer (first dried film as afirst layer) 101A serving as the inner peripheral surface is formedusing the ultrafine alumina particles as the slurry and themulti-layered backup layer 105A made of the slurry layer and the stuccolayer formed using the stucco particles, in which the fine particles,the medium particles, and the coarse particles are mixed with each otherwith a predetermined mixing ratio, is formed on the outside of the primelayer 101A.

In addition, as described above, the prime layer may be the prime layer101B including the slurry layer and the stucco layer added with thestucco particles as the stucco material, in which the fine particles,the medium particles, and the coarse particles are mixed with each otherwith a predetermined mixing ratio (see FIG. 2).

Example 1

The method of producing the mold and the casting method of the presentembodiment will be described below using Examples. Further, in thefollowing Examples, a front wax pattern formed with an outer mold was amember having a width of 30 mm, a thickness of 8 mm, and a length of 300mm, and a prime layer (first dried film) formed from a slurry layer anda multi-layered backup layer made of slurry and a stucco material areformed in the wax pattern, thereby producing a mold.

Zircon powders of 350-mesh were added to the slurry of a silica sol(SiO₂, having a particle size of 20 nm and a solid content of 30%) ofhigh purity ultrafine particles, thereby forming slurry for a precisioncasting mold.

Further, at the same time, a silicon-based substance as an antifoamingagent of 0.01% and a wettability improving agent of 0.01% were added tomake as in-use slurry.

A wax body having a width of 30 mm, a thickness of 8 mm, and a length of300 mm was prepared, after the wax body was immersed and then pulled upinto/from the obtained in-use slurry, thereby adhering the in-use slurryto the surface of the wax, excess in-use slurry was dropped and a primelayer (first dried film) of the slurry was obtained on the surface ofthe wax body by a drying treatment.

Next, in order to obtain a second dried film, the wax body having theprime layer was immersed and then pulled up into/from the in-use slurryand excess in-use slurry was dropped.

The alumina stucco particles having the particle size distribution, inwhich the mixing ratio of the fine particles having a particle size of50 to 500 μm was 1; the mixing ratio of the medium particles having aparticle size of 0.5 to 2 mm was 5; and the mixing ratio of the coarseparticles having a particle size of 2 to 4 mm was 15, were adhered tothe wet slurry and then were dried, so that a second dried film (firstbackup layer) was formed.

The similar operation as the second dried film (first backup layer)forming process was repeated six times, so that a molded body having amulti-layered backup layer was obtained to have a thickness of about 10mm.

The obtained dried molded body was put in an autoclave of 150° C., sothat the wax was melted and then was discharged.

Thereafter, the wax pattern was subjected to a heat treatment at 1000°C., thereby obtaining the mold of Example 1.

Example 2

A mold of Example 2 was obtained by the similar operation as in Example1 except for using spinel stucco particles as a stucco material havingthe particle size distribution in which the mixing ratio of the fineparticles having a particle size of 50 to 500 μm was 1; the mixing ratioof the medium particles having a particle size of 0.5 to 2 mm was 6; andthe mixing ratio of the coarse particles having a particle size of 2 to4 mm was 18 in Example 1.

Example 3

Zirconia slurry (YSZ) as slurry was used for slurry for a precisioncasting mold by adding zircon powders of 350-mesh as flour in Example 1.

A mold of Example 3 was obtained by the similar operation as in Example1 except for using mullite stucco particles as a stucco material havingthe particle size distribution in which the mixing ratio of the fineparticles having a particle size of 50 to 500 μm was 1; the mixing ratioof the medium particles having a particle size of 0.5 to 2 mm was 4; andthe mixing ratio of the coarse particles having a particle size of 2 to4 mm was 12.

Comparative Example

For comparison, a trial production of a mold of Comparative Example wassimultaneously performed using slurry, in which zircon particles havingan average particle size of 0.8 mm were used stucco particles, in thesimilar operation as in Example.

[Test]

A test piece for strength having a size 10 mm×50 mm and a thickness of 5mm was worked from the obtained mold of Example 1 and the mold ofComparative Example was subjected to a high-temperature strength test.

From the test result, the test piece was broken at 150 MPa in Example 1.

From the test result, the test piece was broken at 170 MPa in Example 2.

From the test result, the test piece was broken at 150 MPa in Example 3.

In contrast, the test piece was broken at 100 MPa in the related art.

Here, the strength test was performed based on “bending strength ofceramics (1981) by JIS R 1601.

As a result, it was confirmed that the strength was improved by 50% inExample 1, the strength was improved by 70% in Example 2, and thestrength was improved by 40% in Example 3.

By using the stucco particles as the stucco material having the particlesize distribution in which the mixing ratio of the fine particles havinga particle size of 50 to 500 μm is 1; the mixing ratio of the mediumparticles having a particle size of 0.5 to 2 mm is 2 to 16; and themixing ratio of the coarse particles having a particle size of 2 to 4 mmis 5 to 40, it is possible to improve the strength of the obtained mold.

Thus, the particle size distribution of the stucco material iscontrolled, so that it is possible to produce the mold of high strength.By the improvement of the strength of the mold, the mold can be thinned.As a result, since the temperature gradient can be increased duringsolidification, it is possible to improve the cast product yield and toimprove the strength properties.

In addition, from the improvement of the strength, it is possible toreduce the number of mold-formed layers (adhesion of the wax pattern tothe surface of the slurry and the repetition operation of the drying),to shorten the mold production period, and to reduce the productioncost.

REFERENCE SIGNS LIST

-   -   12, 22 a, 22 b METAL MOLD    -   12 a CONVEX PORTION    -   14, 26 ARROW    -   16 CERAMIC SLURRY    -   18 CORE    -   20, 70 FIRING FURNACE    -   24, 64 SPACE    -   28 WAX    -   30 WAX PATTERN    -   32 SPRUE    -   40 SLURRY    -   60, 92 AUTOCLAVE    -   61 OUTER MOLD    -   61 a FRAGMENT    -   62 DISSOLVED WAX    -   72 MOLD    -   80 MOLTEN METAL    -   90, 100 CAST PRODUCT    -   94 DISSOLVED CORE    -   101A, 101B PRIME LAYER    -   102 SLURRY LAYER    -   103 STUCCO LAYER    -   104-1 FIRST BACKUP LAYER    -   104-n n-TH BACKUP LAYER    -   105A, 105B MULTI-LAYERED BACKUP LAYER

1. A precision casting mold which is used to produce a cast product,comprising: a core having a shape corresponding to an internal hollowportion of the cast product; and an outer mold corresponding to a shapeof an outer peripheral surface of the cast product, wherein the outermold is made up of: a prime layer which is formed on an inner peripheralsurface and is formed from a slurry film obtained by drying slurry forthe precision casting mold; and a multi-layered backup layer which isformed on the outside of the prime layer by repeatedly forming a backuplayer obtained by forming and drying a slurry layer formed from theslurry for the precision casting mold and a stucco layer in which stuccoparticles as a stucco material having particle size distribution, inwhich a mixing ratio of fine particles having a particle size of 50 to500 μm is 1; the mixing ratio of medium particles having a particle sizeof 0.5 to 2 mm is 1 to 16; and the mixing ratio of coarse particleshaving a particle size of 2 to 4 mm is 1 to 40, are adhered to theslurry layer.
 2. The precision casting mold according to claim 1,wherein the prime layer has a stucco layer in which stucco particles asa stucco material having particle size distribution, in which a mixingratio of fine particles having a particle size of 50 to 500 μm is 1; amixing ratio of medium particles having a particle size of 0.5 to 2 mmis 1 to 16; and a mixing ratio of coarse particles having a particlesize of 2 to 4 mm is 1 to 40, are adhered to the slurry layer formedfrom the slurry for the precision casting mold.
 3. A method of producinga precision casting mold which is used to produce a cast product, themethod comprising: a first film forming process in which a precisioncasting wax pattern is immersed and pulled up into/from slurry for theprecision casting mold and then a drying treatment is performed, therebyforming a prime layer, which is formed from a slurry film, on a surfaceof the wax pattern; a second film forming process in which stuccoparticles as a stucco material having particle size distribution, inwhich a mixing ratio of fine particles having a particle size of 50 to500 μm is 1; a mixing ratio of medium particles having a particle sizeof 0.5 to 2 mm is 1 to 16; and a mixing ratio of coarse particles havinga particle size of 2 to 4 mm is 1 to 40, is sprinkled on a surface ofthe slurry after the wax pattern formed with the prime layer is immersedand pulled up into/from the slurry for the precision casting mold andthen a drying treatment is performed, thereby forming a backup layer; amolded body forming process in which the second film forming process offorming the backup layer is repeated more than once, thereby obtaining amolded body formed with a multi-layered backup layer; a wax removingprocess in which wax of the wax pattern is melted and removed from theobtained molded body; and a mold firing process in which the molded bodyobtained after the wax removal is subjected to a firing treatment,thereby obtaining a mold.
 4. The method of producing the precisioncasting mold according to claim 3, wherein the stucco particles as astucco material having particle size distribution, in which a mixingratio of fine particles having a particle size of 50 to 500 μm is 1; amixing ratio of medium particles having a particle size of 0.5 to 2 mmis 1 to 16; and a mixing ratio of coarse particles having a particlesize of 2 to 4 mm is 1 to 40, is adhered to the slurry layer formed fromthe slurry for the precision casting mold to form a stucco layer and thestucco layer is dried during the first film forming process.